If you are on Windows and don't know if you have a 64-bit or 32-bit system, just pick the Windows (32-bit) link. The filenames of the installer versions end with ‘-msi.zip’
Mac Builds are created on a 2.8 GHz Intel Core 2 Duo, 4 GB 1067 MHz DDR3 MacBook Pro running Mac OS X Version 10.6.9 (Snow Leopard).
The Universal builds are 32-bits and 64-bits and support Intel infrastructures.